Tractors are currently used that are equipped with gripping devices making it possible to lift the nose gear of the airplane, so as to tow it, the gear being, as we know, made up of a pair of wheels each comprising one tire, the pair of wheels being fixed to the end of a leg pointing downward from the nose of the aircraft.
One known gripping system for a tractor comprises a hinged longitudinal arm that extends at the inlet of the gripping system, and that is intended to be placed at the rear of the nose gear of the airplane. This longitudinal arm closes on the wheels so as to tighten the nose gear. Opposite the longitudinal arm, a strip in the shape of a shovel is transversely fixed to the tractor slightly above the ground, and is capable of pivoting under the action of a cylinder. The strip therefore makes it possible to lift the front wheels of the airplane, immobilized against the walls of the longitudinal arm and the shovel-shaped strip. Such a device is used on a tractor of the tow barless type: for example, a TPX model tractor of the TLD brand™.
Similar devices exist. For example, systems are known where the hinged longitudinal arm can be replaced by hinged gates that are intended to be placed on both sides of the nose gear of the airplane. Document WO/2008/139437 presents one such system.
Today, tractors are used equipped with such devices to perform airplane driving operations. Two types of driving operations are commonly performed. There is first the so-called “push-back” type, which consists of moving airplanes loaded with passengers (or freight) and fuel away from the jet bridges and other stationary facilities so as to put them in the independent driving position. There is also a so-called “maintenance towing” operation, which consists of moving an empty airplane toward a hangar where maintenance and upkeep operations are performed on the airplane.
In all other cases where the airplane performs a driving operation, the airplane is in the independent driving position; it moves using its own means, i.e. owing to the thrust of its reactors. In particular, the airplane is in the independent driving position during the “taxiing out” phase and/or the return phase. The driving of the airplane in that case is the responsibility of the pilot, who adjusts the airplane's speed only by using the primary brakes of the airplane, the thrust provided by the reactors remaining constant. During this phase when the airplane is driving toward the takeoff runway, the speed of the airplane is approximately 20 knots, i.e. a speed of approximately 37 km/h. The average waiting time of an airplane before it can take off is 20 min., but this period may sometimes exceed 1 hour. And throughout that entire waiting time, the reactors continue to run and consume fuel.
It has been considered to substitute the use of the reactors with a tractor during this so-called “taxiing out” phase. The operation is then referred to as “dispatch towing.” Tests have been performed in this sense, and it has been possible to observe that the fuel consumption of the tractor is considerably lower than what the reactors of the airplanes would have consumed if they had been used.
Despite these fuel savings, the tests have been deemed unacceptable for the following reasons. First, the existing tractors are too slow. Airports are overloaded, and slowing down the routing of the airplanes toward the takeoff runways is inconceivable. Also, the current gripping devices are not adapted to an operational context where it is important for problems to be able to be resolved quickly. In particular, the current mechanisms do not make it possible to unload the airplane quickly in the event the tractor breaks down, which causes a slowdown or even blockage of other airplanes. Any delay is extremely costly for the airlines. Also, the loads and fatigues caused on the nose gear of the airplane are too high during the “dispatch towing” phase. The lifetime of the landing nose gear is thus greatly reduced. For this reason, airplane builders have limited the number of maneuvers that can be performed in this way, some going so far as to prohibit tractors from performing this dispatch towing operation. The airlines have consequently renounced the use of tractors for the taxiing phase. In addition to these economic and technical considerations, there are also legal considerations. Liability is currently transferred to the pilot once the reactors are turned on, and the driver of the tractor is then released from all liability. The liability of driving an airplane on the takeoff runway would then fall to the driver of the tractor, which is inconceivable for airlines and airport managers.
Document WO/2008/139440 presents an airplane tractor making it possible to perform the taxiing phase by allowing the pilot to check the direction and speed of the tractor. However, this airplane tractor comprises a complex gripping system; many actuators are necessary to install the nose gear of the airplane on the tractor. The loading/unloading steps of the airplane are therefore too long and complex. Furthermore, the large number of actuators makes it difficult and excessively time-consuming to unload the airplane in the event the tractor breaks down.